Injection Molding Process for Molding Mechanical Interlocks Between Molded Components

ABSTRACT

A two-shot or multi-shot multi-material injection molding process is provided. The process allows dissimilar materials to be injection molded to form a single, injection molded part by creating a structural interlock between the materials to prevent the materials from separating. The structural interlock is formed by forming at least one interlock cavity adjacent to a interfacial surface of a first portion of a molded part molded from a first material, and injecting a second, different material into the mold so that the second material flows into the interlock cavity and fills it. Solidification of the second material in the interlock cavity formed by the first material creates the structural interlock between the two materials.

RELATED APPLICATIONS

This patent application makes reference to, claims priority to andclaims benefit from U.S. Provisional Patent Application Ser. No.60/746,438 filed on May 4, 2006.

FIELD OF THE INVENTION

The present technology relates to a method of molding differentmaterials to form an individual injection molded part. Moreparticularly, the present technology relates to an injection moldingmethod that creates a structural interlock between two differentmaterials that allows the two different materials to be used to form asingle, injection molded part.

BACKGROUND OF THE INVENTION

Consumer are demanding smaller bulk packages that incorporate greaterfunctionality (i.e., one-by-one product presentation and resealability).These bulk packages, especially bulk packages that must also have otherfunctional requirements, such as moisture-resistance and resealability,is particularly challenging to produce because the functionalrequirements often necessitate the use of multiple parts and materials.However, the use of fasteners to join components together adds to thecomponent count and, most importantly, takes up valuable space.

Two-shot or multi-shot injection molding allows different materialshaving different functional properties to be molded into a single partwithout the need to use fasteners to join the materials together. Thetwo materials are typically joined to each other by means of a welddefined by the interface solidification of melted portions of the twomaterials. In order to form such a weld, however, the differentmaterials must be chemically similar or compatible. This limits theselection of materials that can be used to fabricate the molded part.

There is still a need for an injection molding method that enablesmechanical interlocking to occur between dissimilar materials, therebymaximizing the functionality of the component part without regard tochemical similarity or compatibility of the materials, and without theneed to employ separate fasteners or utilize adhesives.

SUMMARY OF THE INVENTION

One aspect of the present technology is directed to a method of moldingthat creates a structural interlock between two different materials.

Another aspect of the present technology is directed to an injectionmolding process that employs design characteristics that enablemechanical interlocking to occur between dissimilar materials withoutthe use of fasteners or adhesives.

A further aspect of the present technology is a two-shot or multi-shotinjection molding process wherein a first material is injected into amold cavity to form a first portion of a molded part. The first portionincludes an interfacial surface and at least one interlock cavity formedadjacent to the interfacial surface. A second material is injected intothe mold cavity so that the second material contacts the interfacialsurface and flows into the at least one interlock cavity. Solidificationof the second material in the at least one interlock cavity formed inthe first portion of the molded part creates a mechanical interlockbetween the first and second materials which prevents the two materialsfrom being separated, and results in an injection molded part formedfrom dissimilar materials without the need for fasteners or adhesives.

In one embodiment of the molding process described herein a passiveinterlock is created wherein the at least one interlock cavity has anopening at the interfacial surface to allow the second material to flowinto the interlock cavity.

In another embodiment of the molding process described herein, an activeinterlock is created wherein the at least one interlock cavity isblocked by a thin wall formed from the first material, and fill pressurefrom the second material breaches the wall, thereby allowing the secondmaterial to flow into the at least one interlock cavity.

Formation of the mechanical interlock advantageously allows dissimilarmaterials to be used in forming an injection molded part therebyallowing the selection of materials based upon the functional propertiesor characteristics needed without regard to chemical similarity.However, the mechanical interlock may be used to join similar materialswhere material adhesion does not provide enough strength. For example,similar materials may include polypropylene as the first material and apolypropylene impregnated with an electrically conductive compound(e.g., carbon black) as the second material.

Other advantages and features of the present invention will becomeapparent from the following detailed description of the invention, fromthe claims, and from the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. A1 is a perspective view of a two-shot injection molded part madeby one embodiment of the process of the present technology.

FIG. A3 is a detailed view of the mechanical interlock between the twomaterials forming the injection molded part shown in FIG. A1.

FIG. A4 is a cutaway view of the first material forming a portion of theinjection molded part and the interlock cavities for receiving thesecond material; the molding cavity is shown in section.

FIG. A5 is a cutaway view of the second material filling a second moldand flowing into the interlock cavities formed by the first material.

FIG. A6 is a detailed view of a partially filled interlock cavity shownin FIG. A5.

FIG. A7 is a cutaway sectional view of the mold cavity for molding thefirst material.

FIG. B1 is a perspective view of a second embodiment of a two-shotinjection molded part made in accordance with the present technology.

FIG. B2 is a cross-sectional view of the injection mold for theembodiment shown in FIG. B1, but showing the portion of the injectionmolded part and the interlock cavities formed by the first material.

FIG. B3 is a cross-sectional view of the injection mold, illustratingthe second material flowing into the interlock cavities formed by thefirst material.

FIG. B4 is a detailed view of a partially filled interlock cavity shownin FIG. B3.

FIG. B5 is a cross-sectional view of the injection molded part shownFIG. B1, illustrating the interlock cavities completely filled by thesecond material.

FIG. B6 is a detailed view of a filled interlock cavity shown in FIG.B5.

FIG. C1 is a perspective view of another embodiment of a two-shotinjection molded part made in accordance with the present technology.

FIG. C3 is a cross-sectional view taken along lines C5 in FIG. C1,illustrating the second material flowing into the interlock cavitiesformed by the first material.

FIG. C4 is a detailed view of a partially filled interlock cavity showin FIG. C3.

FIG. C5 is a cross-sectional view taken along lines C5 in FIG. C1,illustrating the interlock cavities completely filled by the secondmaterial.

FIG. C6 is a detailed view of a filled interlock cavity shown in FIG.C5.

FIG. D1 is a perspective view of a two-shot injection molded part madeby an alternative embodiment of the process of the present technology.

FIG. D3 is a detailed view of the mechanical interlock between the twomaterials forming the injection molded part shown in FIG. D1.

FIG. D4 is a cutaway view of the first material forming a portion of theinjection molded part shown in FIG. D1 and the interlock cavities forreceiving the second material, with the interlock cavities closed bywalls formed from the first material; the mold cavity is shown insection.

FIG. D5 is a cutaway view of the second material breaking the wallsformed by the first material and flowing into the interlock cavitiesformed by the first material.

FIG. D6 is a detailed view of a partially filled interlock cavity shownin FIG. D5.

FIG. E1 is a top plan view of another embodiment of an injection moldedpart made by the process of the present technology.

FIG. E2 is a side view of the injection molded part of FIG. E1.

DETAILED DESCRIPTION OF THE INVENTION

The present technology describes methods for molding a molded partformed from at least two materials that exhibit different chemicaland/or physical properties. One of the materials is molded to form afirst portion of the molded part which includes an interfacial surfaceand at least one interlock cavity adjacent to the interfacial surface.The other material is molded to form the remainder of the molded partand flows into the interlock cavity created in the first portion of themolded part. When the second material solidifies within the interlockcavity, it creates a mechanical interlock at the interfacial surfacethat prevents the two materials from being separated. The mechanicalinterlock is not dependent on adhesion between the materials.

In one embodiment of the present technology, a passive interlock iscreated at the interfacial surface by forming the interlock cavity so asto have an opening at the interfacial surface that allows the secondmaterial to flow into the interlock cavity. In another embodiment of thepresent technology, an active interlock is created at the interfacialsurface by forming the interlock cavity so that a thin wall of firstmaterial separates the interlock cavity from the mold section receivingthe second material. Fill pressure from the second material shot is usedto breach the thin wall, thereby allowing the second material to flowinto the interlock cavity. Each type of interlock can be created indifferent ways to form both butt joints and lap joints betweendissimilar materials.

The formation of the interlock cavities in the first portion of themolded part followed by the molding and solidification of the secondmaterial within the interlock cavities has several advantages. Nomolding undercut is formed in forming the interlock cavities. In moldingprocesses, the molding of undercuts often is considered undesirablebecause undercuts make the molded part more difficult to extract fromthe mold. Typically, the part must be molded from a flexible material inorder to facilitate extraction of the part from the mold, which limitsthe choice of materials for the part, or the mold is complicated todesign and manufacture, thereby increasing the cost of production of thepart. In the present process, however, the interlock cavities are formedby pins that can easily be removed from the mold cavity, therebysimplifying the mold design.

Although the molding method described herein is particularly suitablefor two-shot or multi-shot injection molding processes, the method canalso be used in overmold processes. Using an overmolding process, apreviously molded part is inserted into a mold and a second material isovermolded about the molded part. The use of mechanical interlocks,especially with materials that do not adhere together, are useful injoining the overmolded component to the previously molded part.

The materials that can be used to form the injection molded part can bevirtually any polymeric material that is capable of being injectionmolded. If the injection molded part is to be used in a package orcontainer the polymer materials must also be compatible with the productto be stored in the container. Suitable polymeric materials includepolyethylene (PE—high density, low density, LLD, VLLD), polypropylene(PP), polyvinyl chloride (PVC), high impact polystyrene (HIPS), cyclicolefin co-polymer (CoC) polyethylene vinyl acetate (EVA), polystyrene(PS), polycarbonate (PC), polyester terephthalate (PET), polyamide(nylon), acetal copolymer or homopolymer resin, and liquid crystalpolymer.

As used herein, “dissimilar” means materials with different physicaland/or chemical properties. Dissimilar materials may be of a differentgrade of a thermoplastic resin where each grade has specific physical orchemical properties. For example, a co-polymer (e.g., ethylene vinylacetate co-polymer) may have different properties based on the ratio(and arrangement) of the co-polymer components.

In one embodiment, one of the selected materials for forming a portionof the injection molded part can be an active polymer composition thatabsorbs or releases a gas. For example, the active polymer compositionmay incorporate a desiccant. Suitable desiccants include, but are notlimited to, silica gel, molecular sieve, calcium carbonate and naturallyoccurring clay compounds, including, but not limited to montmorilloniteclay.

Alternatively, the desiccant composition includes one or more of thefollowing desiccant plastic compositions comprising formulations thatare used to mold shaped articles comprising 2-phase and 3-phasecompositions. A 2-phase composition is one that comprises a desiccantand a polymer. A 3-phase composition is one that comprises a desiccantand at least 2 immiscible polymers.

The polymer is preferably selected from a group of thermoplastics thatinclude polyolefins (for example: polyethylene (LDPE, LLDPE, HDPE andpolypropylene) may be used. Suitable 3-phase desiccant entrained plasticcompositions include, but are not limited to, the desiccant plasticsdisclosed in one or more of the following U.S. Pat. Nos. 5,911,937,6,214,255, 6,130,263, 6,080,350 and 6,174,952, 6,124,006, and 6,221,446.These references are incorporated herein by reference.

Particular combinations of dissimilar polymers that are envisaged foruse in the present two-shot injection molding process include, but arenot limited to, a nylon and a liquid crystal polymer material, apolystyrene and an acetal copolymer or homopolymer resin, and adesiccant entrained plastic and an acetal resin. For example, a partthat needs to have anti-static properties in one area and hightemperature resistance in another area could be molded from a nylonmaterial for its anti-static properties and a liquid crystal polymer forits heat resistance properties. As another example, a part that needs tohave moisture resistance in one area and provide a bearing surface inanother area could be molded from a desiccant entrained plastic for theportion that must have moisture resistance and from an acetal resin toform the bearing surface. In a further example the exposed portion ofthe part can be composed of polycarbonate and the interior portion ofthe part could be composed of desiccant plastic. The polycarbonateprotects the desiccant plastic portion of the part from abrasion and/ordusting. Other material combinations will occur to one of skill in theart.

Various embodiments of the molding method of the present invention willnow be discussed with reference to the drawings. It is to be understoodthat the invention is not intended to be limited to the embodimentsdescribed herein, and the scope of the invention will be pointed out inthe appended claims.

A two-shot injection molded part 10 made according to one embodiment ofthe method of the present invention is illustrated in FIGS. A1-A7. Theinjection molded part 10 is formed by injecting a first material, whichcan be, for example, a nylon, into a mold cavity 12 to form a firstportion 20 of the injection molded part. The mold cavity 12 includes aplurality of pins 16 placed adjacent to one wall of the mold cavity 12,and intersecting what will become the interface between the first andsecond materials. When the first material is injected into the moldcavity 12, it flows partially around the pins, resulting in a pluralityof interlock cavities 24 in the first portion that each have an opening26 at the interfacial surface 28 of the molded first portion. Although aplurality of interlock cavities are illustrated in the first portion 20,it will be appreciated that the number of interlock cavities could beone, two, or more cavities depending upon the size of the part, the sizeof the cavity, and the materials selected to form the part.

It is important that the opening 26 to each interlock cavity has a sizethat is less than the diameter of the interlock cavity, alternativelyless than half the diameter of the interlock cavity so that the openingis restricted or narrow. This restricted opening is wide enough to allowthe second material to flow into the interlock cavity, but narrow enoughto act as a mechanical anchor that prevents the second material frombeing pulled apart from the first material after solidification, asexplained further below.

After molding the first material to form the first portion of theinjection molded part, the mold is opened and rotated to a second moldcavity 14, the mold is closed, and a second material, which can be, forexample, a liquid crystal polymer material, is injected into the moldcavity 14. The second material contacts the interfacial surface 28 ofthe molded first portion and flows into the interlock cavities 24 formedin the first portion 20, as shown in FIGS. A5 and A6, forming a secondportion 22 of the molded part. A mechanical interlock 29 is then createdbetween the first and second materials by the cooling and solidificationof the second material in the interlock cavities formed in the firstmaterial, as shown in FIGS. A1 and A3.

A two-shot injection molded part made according to another embodiment ofthe injection molding process of the present invention is illustrated inFIGS. B1-B6. The B1-B6 embodiment would be suitable for a part thatneeds to have moisture resistance in one area and provide a bearingsurface in another area. The injection molded part 30 has a firstportion 32, that is molded from a first material and that overlaps asecond portion 34. The second portion 34 is molded from a secondmaterial that differs from the first material in at least one property.The injection molded part 30 is formed by injection molding the firstmaterial in a mold cavity to form the first portion 32 of the injectionmolded part. The mold cavity is provided with a plurality of generallyfrustaconically-shaped pins that project downwardly from the top of themold cavity (as oriented in FIG. B2). The frustaconically-shaped pinshave their base end at the top of the mold cavity, while the smallerdiameter end intersects what will become the interface between the firstand second materials.

When the first material is injected into the mold cavity, it flowsaround the pins, resulting, upon solidification, in a plurality ofinterlock cavities 36 that extend completely through the molded firstportion. Because of the shape of the pins, the resulting interlockcavities 36 have an opening 38 at the interfacial surface 35 of themolded first portion that is smaller than the opening 39 at the oppositeend of the interlock cavity, as shown in FIG. B2.

After molding the first material to form the first portion of theinjection molded part, the pins are removed. The mold is opened androtated to a second mold cavity 40, the mold is closed, and the secondmaterial is injected into the second mold cavity. The second materialfills the second mold cavity, contacts the interfacial surface 35 andflows into the interlock cavities 36 formed in the first portion, asshown in FIGS. B3 and B4. Solidification of the second material in theinterlock cavities formed in the first material creates a mechanicalinterlock 48 between the first and second materials, as illustrated inFIGS. B5 and B6, by forming a neck portion of solidified second materialthat is more narrow than the diameter of the filled interlock cavity.

Another embodiment of a two-shot injection molded part made inaccordance with the present process is illustrated in FIGS. C1-C6. Thetwo-shot injection molded part 50 has a first portion 52, molded from afirst material, and a second portion 54 molded from a second materialthat differs from the first material in at least one property. Theembodiment illustrated in FIGS. C1-C6 is suitable for a molded partwherein the second portion is comprised of a desiccant entrained plasticand the first portion is comprised of a polycarbonate to provideprotection for the desiccant plastic portion and protect it fromabrasion and/or dusting. The first portion 52 is bowl-shaped and has aninner sidewall 56 that forms an interfacial surface and an outersidewall 58.

The injection molded part 50 is formed by injection molding the firstmaterial in a mold cavity 60 to form the first portion of the injectionmolded part. The mold cavity is provided with a plurality of pins thatproject inward from the wall of the mold cavity. Each pin has a largerdiameter end that is adjacent to the mold cavity wall and a smallerdiameter end that intersects what will become the interface between thefirst and second materials.

Similar to the embodiment shown in FIGS. B1-B6, when the first materialis injected into the mold cavity, it flows around the pins, resulting,upon solidification, in a plurality of interlock cavities 62 that extendcompletely through the first portion, from the inner sidewall 56,forming the interfacial surface, to the outer sidewall 58. Eachinterlock cavity 62 has an opening 64 at the interfacial surface thathas a diameter that is smaller than the diameter of the opening at theouter sidewall 58.

After forming the first portion 52, the mold is opened and rotated to asecond mold cavity. The mold is then closed and the second material isinjected into the second mold cavity to form the second portion 54 ofthe molded part. The second material fills the second mold cavity,contacts the interfacial surface, and flows into the interlock cavities62 formed in the first portion 52, as shown in FIGS. C3 and C4.Solidification of the second material in the interlock cavities formedin the first portion creates a mechanical interlock 68 between the firstand second materials, as illustrated in FIGS. C5 and C6.

A further embodiment of the injection molding process of the presentinvention, illustrating the use of an active interlock, is describedwith reference to FIGS. D1-D6. The injection molded part 70 has a firstportion 72, formed from a first material, and a second portion 74 formedfrom a second material that differs from the first material in at leastone property. The molding of the first and second materials is similarto the process described in connection with FIGS. A1-A7, except that thepins are positioned in the mold cavity so that they are adjacent to butdo not intersect what will become the interface between the first andsecond materials. When the first material is injected into the moldcavity 80, it flows completely around the pins, resulting, uponsolidification, in a plurality of interlock cavities 76 in the firstportion 72 that are closed off from the second mold cavity by a thinwall 78 formed from the first material as shown in FIG. D4. The wall hasa thickness ranging from about 0.005 to about 0.010 inches (0.125 mm to0.250 mm).

When the second material is injected into the second mold cavity, fillpressure from the injection breaks the wall 78, allowing the secondmaterial to flow into the interlock cavities 76 formed in the firstportion 72, as shown in FIGS. D5 and D6. Solidification of the secondmaterial in the interlock cavities 76 creates a mechanical interlock 82between the first and second materials. Further, when the thin-walledsection of the interlock cavity is broken, the second material flowsaround the broken portions of the walls to create additional mechanicalanchors 84, as shown in FIGS. D1 and D3, that further prevent the twomaterials from being pulled apart.

Another embodiment of an injection molded part made in accordance withthe method of the present technology is shown in FIGS. E1 and E2. Themolding process described in connection with FIGS. A1-A7 is used to moldthe part 90. A first portion 92 is molded from a first material, such asa polycarbonate, that can flex, as shown in FIG. E2, and has a memorythat enables the first portion of the part to be. used as a type ofspring. A second portion 94 is molded from a second material, such as adesiccant entrained plastic.

The invention has now been described in such full, clear, concise andexact terms as to enable any person skilled in the art to which itpertains to practice the same. It is to be understood that the foregoingdescribes preferred embodiments and examples of the invention, and thatmodifications may be made therein without departing from the spirit orscope of the invention as set forth in the claims.

1. A method of molding a molded part formed from at least two materialscomprising the steps of: (a) injecting a first molten material into amold so that the first material forms a first portion of the moldedpart, the first portion of the molded part having an interfacial surfaceand at least one interlock cavity formed adjacent to the interfacialsurface; (b) injecting a second molten material into the mold such thatthe second material contacts the interfacial surface and flows into theinterlock cavity adjacent to the interfacial surface, and (c) allowingthe second material to cool and solidify, whereby solidification of thesecond material in the interlock cavity forms a mechanical interlockbetween the first material and the second material that prevents thefirst and second materials from being separated.
 2. The method of claim1, wherein the interlock cavity has an opening at the interfacialsurface that is less than the diameter of the interlock cavity.
 3. Themethod of claim 2, wherein the interlock cavity has an opening at theinterfacial surface that is less than one-half the diameter of theinterlock cavity.
 4. The method of claim 1, wherein the interlock cavityis closed by a wall formed from the first material, the wall having athickness in the range of about 0.005 to about 0.010 inches, and whereinfill pressure from the injection of the second material into the moldbreaches the wall to permit the second material to flow into theinterlock cavity.
 5. The method of claim 1, wherein the first portion ofthe molded part has a plurality of interlock cavities formed adjacent tothe interfacial surface.
 6. The method of claim 1, wherein at least oneof the first or second materials comprises a thermoplastic polymer. 7.The method of claim 1, wherein the first and second materials aredissimilar.
 8. The method of claim 1, wherein the first and secondmaterials are similar.
 9. The method of claim 1, wherein the firstmaterial comprises a polycarbonate resin and the second materialcomprises a desiccant entrained polymer.
 10. The method of claim 1,wherein at least one of the first or the second materials comprises adesiccant entrained polymer.
 11. The method of claim 10, wherein thedesiccant entrained polymer comprises at least one polymer and adesiccant.
 12. The method of claim 11, wherein the desiccant entrainedpolymer comprises at least two immiscible polymers and a desiccant. 13.The method of claim 1, wherein the at least one interlock cavity isformed by a pin inserted into the mold.
 14. The method of claim 1,wherein the first and second materials are injection molded in atwo-shot injection mold.
 15. The method of claim 1, wherein the firstand second materials are injection molded in an overmolding process. 16.An injection molded part formed from at least two materials comprising:(a) a first material that forms a first portion of the molded parthaving an interfacial surface and at least one interlock cavity formedadjacent to the interfacial surface; (b) a second material that forms asecond portion of the molded part such that the second material contactsthe interfacial surface and fills the interlock cavity adjacent to theinterfacial surface, thereby forming a mechanical interlock between thefirst material and the second material that prevents the first andsecond materials from being separated.
 17. The injection molded part ofclaim 16, wherein the mechanical interlock has a neck that is narrowerthan the diameter of the interlock cavity.
 18. The injection molded partof claim 16, wherein the first portion of the molded part has aplurality of cavities formed adjacent to the interfacial surface. 19.The injection molded part of claim 16, wherein at least one of the firstor second materials comprises a thermoplastic polymer.
 20. The injectionmolded part of claim 16, wherein the first and second materials aredissimilar.
 21. The injection molded part of claim 16, wherein the firstand second materials are similar.
 22. The injection molded part of claim16, wherein the first material comprises a polycarbonate resin and thesecond material comprises a desiccant entrained polymer.
 23. Theinjection molded part of claim 16, wherein at least one of the first orthe second materials comprises a desiccant entrained polymer.
 24. Theinjection molded part of claim 23, wherein the desiccant entrainedpolymer comprises at least one polymer and a desiccant.
 25. Theinjection molded part of claim 24, wherein the desiccant entrainedpolymer comprises at least two immiscible polymers and a desiccant.